An electroacoustic receiver, as used in a hearing aid, typically converts an electric signal to an acoustic sound through a motor assembly having a movable armature. Typically, the armature has one end that is free to move while the other end is fixed to a housing of the receiver. The assembly also includes a drive coil and one or more magnets, both capable of magnetically interacting with the armature. The armature is typically connected to a diaphragm near its movable end. When the drive coil is excited by an electrical signal, it magnetizes the armature. Interaction of the magnetized armature and the magnetic fields of the magnets causes the movable end of the armature to vibrate. Movement of the diaphragm connected to the armature produces sound for output to the human ear.
Digital signal processors (DSP) are also utilized in the manufacture of hearing aids. Hearing aids of this type generally include a DSP, a microphone, a receiver, and an analog-to-digital converter.
The popularity of hearing aids with digital signal processors has created a need for low capacitance receivers. DSP-based hearing aids typically drive the receiver with a pulse width modulated signal having a carrier frequency of 1 to 2 MHz. At these carrier frequencies, parasitic capacitance of the receiver coil adds greatly to the hearing aid's current flow. Thus, precious battery power is wasted. Also, hearing aids provided with switched signal output (such as class D amplification) consume less current when the parasitic capacitance of the receiver is reduced.
There are several well established methods of reducing the capacitance of high frequency inductors. While these methods have been around since the 1940's, they have not been applied in hearing aid components. Low capacitance methods have been avoided in the past for hearing aid receivers, as these methods add to the total coil size and manufacturing effort.
The present invention provides methods of reducing hearing aid receiver coil parasitic capacitance.